This invention relates to a precast concrete structural element and to methods of making and installing same. More particularly, this invention relates to a precast concrete beam element for providing continuous footing support in building and structure foundations and to methods of making the precast element and installing it in building and structure foundations.
Several methods for providing continuous beam footing for wall and floor slab support in building and structural foundations are known in the art. Three of the most popular methods are described below.
One popular method involves excavating a trench, placing edge forms and reinforcement in the trench, and either partially casting the beam and then casting the floor slab or simultaneously casting the beam and floor slab. This method has several disadvantages. For example, the method requires an excavation that is open to weather conditions while reinforcement is being placed in the trench. This often necessitates removal of the reinforcement after inclement weather has passed in order to remove mud and water from the excavation and restore bearing capacity prior to casting. In addition, this method requires field forming of the floor slab edge and the wall ledge. Thus, the accuracy of the slab edge forming, the wall ledge forming and the beam shape are each dependent on the skill of the craftsmen executing the work in the field. Furthermore, the method uses more concrete that would be required simply for structural purposes in order to save the cost of forming a thinner wall thickness that is required structurally. This increase in sectional area of the concrete necessitates an increase in the amount of steel reinforcement required under some building codes. Also, the increase in the bearing width requires additional unnecessary concrete in the upper section of the beam.
A second popular method for providing continuous beam footing to support wall and floor slab edges involves excavating a trench, casting the continuous bearing beam in the trench, forming an upper stem wall section including a support notch for a floor slab, casting the stem wall section, removing the forms, backfilling void areas adjacent to the stem wall, and then casting the floor slab.
This second method offers some advantages over the first method discussed above in that, in the second method, the upper stem wall can be formed to the minimum thickness required for structural needs, thereby saving substantial concrete material if the bearing depth is significant. The second method also allows for a greater difference between finish floor height and the ultimate exterior grade. However, the second method also has several disadvantages. For example, it requires an excavation open to weather conditions as in the first method but in the second method the excavation is open for an even longer period while the stem wall section is formed. The second method requires labor-intensive forming of the stem wall section, often in below grade conditions which may require continuous dewatering to achieve a structurally sound installation. The second method further requires subsequent backfilling and compaction of the void areas adjacent to the stem wall. Moreover, the second method requires either a notch to support the floor slab or steel rods through the inner face form to provide shear dowels into the floor slab. In addition, the accuracy of the slab edge forming, the slab bearing notch, and the stem wall section are each dependent on the skill of the craftsmen executing the work in the field.
A third popular method for providing continuous beam footing to support wall and floor slab edges is similar to the second method discussed above, except that in the third method, the exterior walls (usually masonry) are extended to the top of the bearing beam, followed by floor casting. In an advantage over the second method, the third method eliminates the stem wall forming step. However, the third method requires an extended period of open excavation and, typically, the time required for the installation of the below-grade portion of the exterior wall is even longer than that required to form the stem wall in the second method. Furthermore, installation of the below-grade portion of the exterior wall is labor intensive. In a further disadvantage, the third method requires backfilling and compaction of the void areas adjacent to the below-grade portion of the exterior wall. In addition, accuracy is still dependent upon the skill of the craftsmen executing the work in the field.
A primary object of this invention is to provide an improved concrete beam element which integrates the edge of slab form and the wall ledge to completely eliminate the need for field forming.
Another object of this invention is to provide an improved concrete beam element which is capable of being cast with dowel rods projecting above the wet concrete instead of through the mold.
A further object of this invention is to provide an improved method of making a concrete beam element which does not require field forming.
A still further object of this invention is to provide an improved method of making a concrete beam element wherein the method uses a mold that allows for varying beam heights to accommodate varying beam depths.
Another object of this invention is to provide an improved method of making a concrete beam element wherein the method uses a mold the depth of which can be easily increased to offer additional bearing capacity or stem wall thickness as soil and loading conditions require.
Yet another object of this invention is to provide an improved method of installing a concrete beam element wherein the exposure period of the excavation site to the weather is significantly less than that required in the prior art methods discussed hereinabove.
These objects and others are achieved in the present invention.
One embodiment of the present invention provides a precast concrete beam element for use as a continuous bearing structural foundation member supporting wall and floor slab loads in soil. Another embodiment of the present invention provides a method of making the aforementioned precast structural beam element. In addition, a further embodiment of the present invention provides a method for installing the precast concrete beam element into a building or structural foundation.
The precast structural beam element may include a straight back face, a top surface, a bottom surface, a front face, and first and second opposite side faces disposed between the back and front faces and between the top and bottom surfaces. The front face may include: a first upper surface extending perpendicularly and downwardly from the top surface and being parallel to the back face; a second upper surface which slopes downwardly and inwardly from the first upper surface; a middle surface which is parallel to the back face and which extends downwardly from the second upper surface; a first lower surface which slopes downwardly and outwardly from the middle surface; and a second lower surface which is parallel to the back face and which extends downwardly from the first lower surface and perpendicularly to the bottom surface. The beam element may include a notch formed therein which extends lengthwise along the top surface, and/or the middle surface of the front face has a dapped surface formed therein.
The method of making the beam element may include providing a mold containing: (a) a longitudinally movable lateral side rail having an inner wall for forming the top surface of the beam element; (b) an opposite fixed lateral side rail having an inner wall for forming the bottom surface of the beam element; (c) a first longitudinal side rail disposed between the movable and fixed lateral side rails and having an inner wall for forming the first side face of the beam element; (d) an opposite second longitudinal side rail disposed between the movable and fixed lateral side rails and having an inner wall for forming the second side face of the beam element; (e) an infill plate disposed between the inner walls of the lateral and longitudinal side rails such that an upper face of the infill plate and the inner walls of the lateral and longitudinal side rails define a mold cavity, the upper face of the infill plate being disposed to form the front face of the beam element; and (f) one or more dowel rods projecting upwardly from the mold cavity. The method may also include: filling the mold cavity with a flowable fill material; allowing the flowable fill material to harden to form the beam element; and removing the beam element from the mold cavity.
The method of installing the beam element may include: providing an excavated trench having a bottom surface, inner wall surfaces and an open top surface; (2) suspending the beam element above the trench so that a bottom gap is formed between the bottom face of the beam element and the bottom surface of the trench and a side gap is formed between the inner walls of the trench and the front, back and side faces of the beam element; (3) pouring a flowable fill material into the trench so as to fill the bottom gap and at least a portion of the side gap; and (4) causing the poured material to harden.
Another embodiment of the present invention provides a method for forming a floor slab. The method may include: (1) installing the beam element in accordance with the method above; (2) providing a floor slab-forming location for forming the floor slab, the location being adjacent to the beam element such that the back face of the beam element will serve as an edge form during casting of the floor slab; and (3) casting the floor slab in the location.
A further embodiment of the present invention provides a method of forming a wall slab. The method may include: (1) installing the beam element in accordance with the method above; (2) providing a wall slab-forming location for forming the wall slab, the location being adjacent to the beam element such that the top face of the beam element will serve as an edge form during casting of the wall slab; and (3) casting the wall slab in the location.
The precast concrete beam element may include a unique shape and a bearing surface (defined by the bottom surface of the beam element) for spreading vertical loads into soil and a wall section (defined by the back face of the beam element) having a height sufficient to place the bearing surface at a specified bearing depth in the soil. The precast beam element may also include a formed-in notch to serve as a block ledge to facilitate weathertight wall installation. The beam element may integrate both the slab form edge and the wall ledge, for example, to eliminate the need for field forming.
The precast concrete beam element may be manufactured offsite in a mold capable of changing dimension to cast elements with differing bearing heights. The unique shape of the beam element allows it to be cast with dowel rods projecting above the wet concrete instead of through the mold. In addition to offering adjustable beam height for varying beam depths, the mold depth can be easily increased to offer additional bearing capacity or stem wall thickness as soil and loading conditions require.
The method of installing the precast concrete beam element may involve the simple suspension of the beam element above an excavated trench with a gap being formed between the bottom and sides of the trench and the surfaces of the beam element. As the beam element is suspended above the trench, a flowable fill material is poured into the trench to fill the void areas. When the flowable fill material hardens, the beam element is locked into place, achieving full bearing and lateral stability.
The embodiments of the present invention offer advantages over the prior art. For example, the beam element may be made using an adjustable mold which provides the ability to manufacture beam elements with varying structural capacities. In addition, the particular cross-section of the beam element may provide structural capacity with minimal material and weight. Furthermore, such cross-section may also allow for efficient stacking of the beam elements in the storage yard and may facilitate easy handling for loading and trucking.
Another advantage is that the beam element may be capable of serving as a stayin-place form for the slab edge and the wall ledge. Moreover, the construction site may be prepared while the beam elements are being produced offsite. This facilitates rapid installation of the elements as soon as the site preparation is complete. Furthermore, the flowable fill material may be cast as the beam elements are being installed, thereby greatly reducing the exposure time of the excavation site to inclement weather.
No edge forming of the slab, wall ledge or field forming of the stem wall may be required in making the beam element.
Installation accuracy is assured, for example, since the installation worker can adjust the beam location using an adjustable hanger. The beam element may be grouted and secured into place before the slab is cast, thereby assuring that the edge will not vary as field forms tend to do under the pressure of concrete casting.
Also, the use of special forms to make the beam elements eliminates dependency on skilled labor to assure accurate beam and slab edge dimensions.